1. Field of the Invention
The present invention relates generally to a drive recess formed in the head top surface of a screw, and more particular to a novel compound drive recess permitting the screw to drive various types of drive bits, such as Slot, Phillips (cross), Square, Pozi, and Cross-square. In addition, this invention also can be driven by its tailor-made drive bit (U.S. patent Ser. No. 09/373,022) which gives the compound drive recess the capacity to withstand high driving torques with minimal drive bit slip or cam-out. This invention also relates to screws with compound recesses of U.S. Ser. No. 09/193,489 which has been abandoned.
2. Description of the Related Art
Currently, conventional screws or bolts include a variety of head types, such as countersunk, oval, pan, truss, etc., which can adapt to at least five kinds of drive recesses as shown in FIG. 1, 2, 3, 4 and 5. Element A in FIG. 1 is a slot; element B in FIG. 2 is a cross; element C in FIG. 3 is a cross-square combination; element D in FIG. 4 is a square; and element E in FIG. 5 is a Pozi. Drive recess structures like those mentioned above cannot stand comparatively large torques due to their structural weakness and uneven pressure distribution. The loose fit between the drive recess and the drive bit, which are very common in the above mentioned drive recesses, may produce a large torque causing impaired drive recess or broken drive bit.
U.S. Pat. No. 3,575,080 titled "FASTER WRENCHING MEANS" includes recess composed of inner portions of the pockets (13, 14 and 15); web surface (19, 20 and 21), and a central portion (22). This type of recesses limits the range of available drive bits such as slot drive bits (FIG. 6), cross-square drive bits (FIG. 10), and Phillips drive bits (FIG. 12), and Pozi drive bit (FIG. 14).
Next, U.S. Pat. No. 3,108,623 and 4,187,892 cannot be driven by a drive bit with a fan-shaped tip.